A reassessment of the applicability of Bergmann’s Rule to humans

It is widely accepted that human body size varies in accordance with Bergmann’s Rule, which states that body mass within a species should increase with latitude and cooler temperatures. However, the studies supporting this hypothesis have used samples that include a disproportionately large number of warm-climate populations. Here, we investigated whether the finding that humans conform to Bergmann’s Rule is an artifact of the use of warm climate-biased samples.

Data on adult male mass, stature, geographic location, and mean annual temperature were compiled for 265 populations. The sample was stratified to include four populations for each five degree band of latitude. Regression analysis was used to assess the direction and strength of the relationships between latitude and mean annual temperature on the one hand, and body mass, Body Mass Index (BMI), Ponderal Index (PI), and surface-area-to-body-mass ratio on the other.

When populations from north and south of the equator were analyzed together, Bergmann’s Rule was supported. The anthropometric variables correlated significantly with latitude and mean annual temperature in the majority of analyses. However, when populations were separated by hemisphere, Bergmann’s rule was not supported. In the northern latitude sample, the relationships between BMI, PI, and surface-area-to-body-mass ratio and mean annual temperature were quadratic rather than linear. In the southern latitude sample, none of the anthropometric variables was significantly correlated with latitude or mean annual temperature. These results suggest that it is only in northern latitudes that human body size variation conforms to Bergmann’s rule.

Research funded by the Canada Research Chairs Program, the Canada Foundation for Innovation, the British Columbia Knowledge Development Fund, and Simon Fraser University.